In the food industry, frozen blocks of beef, pork, poultry, fish, shellfish meats and the like are one common form of intermediate or starting material for the manufacture of finely comminuted, thermally set, gel-type products, such as hot dogs, bologna, and simulated shellfish meats. The frozen form of such raw meats allows food processors to be nearer their respective markets, frees them from the concerns of whole animal production, harvesting and processing, and enables inventories of such raw materials to be stockpiled against the possibility of shortages.
A primary quality of such meats intended for use in gel-type products is their ability to form strong gels when comminuted with salt and thermally processed. This gel-forming potential may be referred to as "bind" value and varies as a function of biological factors such as species, muscle type, age of the animal and the like. The native bind potential of any meat can, however, deteriorate as a result of processing and storage of the meat. For example, it is recognized that pre-rigor beef has much higher bind potential than post-rigor beef. Similarly, fresh, properly cleaned and chilled fish also have better gel-forming potential than poorly handled fish. Much of this gel-forming ability can be lost, however, during extended frozen storage, during which muscle protein will denature, i.e. suffer change in its original structure and lose some of its natural desireable qualities.
Maintaining gel-forming potential in meat is presently thought to depend on maintaining the myofibrillar proteins of the muscle tissue as near to the native state as possible. Such maintenance depends on preventing the denaturation of the muscle tissue proteins by the action of heat, microorganisms, enzymes, or extended holding times. Prevention of denaturation requires proper chilling of meats soon after they are slaughtered, rapid processing and freezing, and holding at temperatures as low as are economically feasible.
One type of commercially important frozen meat product for which preserving gel-forming potential is important is surimi, a water washed fish mince used widely in Japan as a precurser for comminuted, gelled fish food products. Basically, surimi comprises a frozen intermediate product produced by carefully and properly filleting fresh fish, mincing, washing and mixing the fish with particular additives, and freezing the mixture in large blocks, after which it can be packed, stored and transported. Surimi is used by Japanese food processors to make a modern version of the traditional Japanese jellied fish cake, "Kamaboko". Kamaboko is a traditional food in Japan, records of which exist from as long as 1500 years ago and which can be made into many varied forms of a final food product. Kamaboko can be steamed, broiled or fried and can be served as meat paste, tubes, balls, noodles, rolls and chipped meat. Of importance with regard to the present invention, the final quality of Kamaboko made from surimi will depend largely on the surimi's quality, making the production and preservation of fish meat in surimi form a major economic consideration in the Japanese food industry.
While proper handling of the minced meat prior to freezing is an important factor in producing high quality surimi and a resulting high quality Kamaboko, it has been known to surimi producers that such proper handling alone is insufficient to prevent denaturation and to maintain the gel-forming potential of the surimi. It has been found, however, that the addition of about 8% by weight of a mixture of sugar (sucrose) and sugar alcohol (sorbitol) followed by fine comminution of the fish meat will preserve the gel-forming properties of the resulting surimi for one year or more in frozen storage (-20.degree. C. or less).
Although the addition of this sucrose-sorbitol mixture is effective as an antidenaturant or "cryoprotective" agent, the relatively large amount required results in an increased caloric content and increased sweetness level in the meat. Although these qualities have become acceptable for Asian consumers, they can be objectionable in products intended for western consumers. Additionally, sucrose can cause a brownish color in a finished fish food product while sorbitol can give the final product a harder, less desirable texture.
Several studies have been made on the effects of various other compounds in preventing the freeze denaturation of frozen fish meat products in attempts to provide acceptable alternatives to the sucrose-sorbitol mixtures. These studies have also focused on the technical aspects of freeze denaturation in an attempt to understand the basic mechanisms by which denaturation takes place.
During these studies, the following compounds and classes of compounds have been tested as antidenaturants for frozen fish food products: sodium glutamate, amino acids, peptides, carboxylic acids, carbohydrates and combinations of various of the listed compounds, along with certain other substances which are generally related to one or more of the listed categories of compounds. None of the compounds studied showed any cryoprotective effects markedly better than the commercially practiced combination of sucrose and sorbitol, and many present problems of cost and side effects given the amounts necessary to prevent denaturation: T. Akahane, Freeze Denaturation of Fish Muscle Proteins (1982) (Doctoral Thesis, Sophia University, Tokyo, Japan); S. Noguchi, The Control of Denaturation of Fish Muscle Proteins During Frozen Storage (1974) (Doctoral Thesis, Sophia University, Tokyo, Japan).
Heretofore, the antidenaturant characteristics thought best for preventing denaturation included small molecular size and specific molecular structure. When tested for their cyroprotective effects during the aforementioned studies, all compounds having larger more randomly structured molecules showed little or no cryoprotective effect whatsoever.
It is therefore an object of the present invention to provide the food industry with an antidenaturant which will protect food during extended periods of storage, but which will also do so with reduced calorie levels and less sweet taste, making the resulting products more acceptable to western consumers.